1. Field of the Invention
The present invention relates to an improvement of a system for deriving the numeral output stored in a register to dynamically drive in a time-division manner a numeral display device in which a plurality of digit display units are arrayed in parallel, and more particularly a system for deriving the numeral output from a circulating register which system may eliminate the abnormal light emission between the adjacent digit places (overlapped display), beat and noise.
2. Description of the Prior Art
In a dynamic display system, a numeral consisting of a plurality of digits may be displayed in a time-division manner by a display device consisting of a plurality of digit display units, and not only the content which is to be displayed but also the digit place in the display device at which the content of the output information is to be displayed are selected during a unit digit time. Therefore a digit is displayed at one digit place in the display device only when the digit to be displayed and the digit place at which the digit is to be displayed are simultaneously selected. In general in the drive system of the type described, the digit place selection in the display device is made from one unit digit time to another, and the display unit at the selected digit place is driven over the full unit digit time. The drive system of the type described is fully disclosed, for instance, in French patent No. 1350840, FIG. 5.
It has been found that the digit place selection pulse is superposed upon the next digit-place-selection pulse and the abnormal light emission occurs, when the fall time of the digit place selection pulse is longer and when the circuit has a high floating capacitance between the wires. This abnormal light emission is clearly observed particularly in case of a seven-bar-segment type display tube.
The foregoing problem is removed in accordance with the present invention which relates to a system for deriving the output stored in a circulating register to display or print a numeral in an electronic desktop calculator, and more particularly a system capable of preventing the decrease in brightness and flicker in a dynamic display system of the type displaying a numeral stored in a register in a series time division scheme.
In the conventional system for deriving the numeral output from a register, a numeral information stored in N-digit shift register are sequentially transferred into a buffer register, and the numeral information stored in the buffer register is transferred into a decoder during one digit time (generally four bit periods). The decoder drives a specific digit place in a numeral display device during one digit time so that the time-division display may be accomplished. Therefore, the display duty of the display device is only 1/N. One digit time is dependent upon the circulation speed of the shift register. Therefore the circulation speed of the register must be increased as the operation speed of a computer is increased. As a result one digit time is shortened, thus it is difficult to obtain the sufficient time for driving the display device. This results in the decrease in brightness and flicker.